In systems for utilizing solar energy, the collectors (heliostats), which are composed of several individual elements in large flat aggregates, are adjusted in their position constantly to track the continually changing position of the sun in order to achieve highest possible efficiency. In one conventional system, the collectors are mounted pivotally about a horizontal axis on a frame, which frame is supported rotatably about a vertical axis by several wheels on a rail laid in a closed circle. However, the structural complexity and cost for the frame and the rail, which must be laid very exactly, can be justified only in very large systems. It is also necessary in such a system to constantly rotatingly readjust the collectors, both about the vertical axis and--independently therefrom--also about the horizontal axis. However, Applicants have recognized as more advantageous an arrangement of a first axis at least approximately directed toward the sun, since then the collectors need be rotatingly readjusted only about a second axis perpendicular to the first axis, while readjusting of the first axis is necessary only from time to time.
Also, this readjusting of the first axis can in effect occur by a pivoting of the collectors about a third axis positioned perpendicular to both the first axis and the second axis.
Therefore, the basic purpose of the invention is to produce an apparatus which is as compact as possible, which can be arranged at any desired inclination on a fixed column and with which the collectors can be rotated about two axes which lie perpendicular to one another. Corresponding purposes, for this use, are to provide for very small rotational speed about the axes (n&lt;3.10.sup.-2 rpm), and for a high resistance to twisting, and, if desired in a given instance, for self-locking near the axes of rotation.
The purposes of the invention are attained by providing an apparatus in which a first drive mechanism is provided which is stationary and includes a housing, an electric motor, a multi-stage planetary gear set, a spur-gear stage and a driven shaft; and a second drive mechanism is provided which is rotatable by reason of having a housing carried at the free end of the driven shaft of the first drive mechanism, the second drive mechanism further having its own electric motor, multi-stage planetary gear set, spur-gear stage and driven shaft, with the driven shaft of the second drive mechanism being directed perpendicular to the driven shaft of the first drive mechanism and carrying at its ends the aggregates to be rotated. In particular, it is possible with a multi-stage planetary gear set to house a high step-down ratio transmission in a small space. Further, the short elastic length of the planetary gear sets arranged one behind the other provides good resistance to unwanted twisting.
A further development of the invention provides that the two drive mechanisms are built the same but permit different transmission ratios by having different spur-gear stages. The resulting substantial standardization of structural parts limits manufacturing cost to favorable levels. A further development of the invention provides that the two drive mechanisms are built the same but permit different transmission ratios, as through an additional spur-gear stage between the electric motor and multi-stage planetary gear set in at least one of the two drive mechanisms, which again permits standardization of parts and cost advantages.
A further development of the invention provides for incorporation into a slide-in unit of the drive motor, multi-stage planetary gear set and driving gear of the respective spur-gear stage, and if present the additional spur-gear stage, of a given drive mechanism, wherein the slide-in unit is insertable as a unit in the housing of the respective drive mechanism. This makes substantially easier the installation and, if necessary, removal of the drive mechanism of a given shaft.
A further development of the invention provides for eccentric reception of a given slide-in unit into the housing of the respective drive mechanism, which permits substantial achievement of the needed freedom from clearances in the drive train, particularly in the tooth system thereof. Freedom from clearance in the drive train is further enhanced by supporting the shaft in its housing by means of bearings that can be adjusted to a clearance-free condition, for example conical-roller bearings. Clearance-free adjustment of the teeth in the axial direction can be obtained through use of gears having conical teeth.
A further development of the invention provides that the last stage of the planetary gear set is a self-locking Wolfrom gearing, which automatically blocks transmission of motion from its output side to its input side therethrough. This further reduces drive system backlash and at the same time fulfills the demand for self-locking, so as to prevent reverse transmission of motion through the drive train and thus prevent unwanted movement of the aggregate as due, for example, to wind loading.